eviously, insulin receptors could be demonstrated in membrane preparations heads and bodies of chick embryo by 4 days of incubation. Binding of beled insulin to brain and liver membranes from 8 to 18 day embryos creases with time of development. Recently, insulin-like growth factor nding was studied in chick embryo tissue. Using labeled multiplication imulating activity peptide and insulin-like growth factors I and II there pears to be specific insulin-like growth factor receptors on brain membrane eparations of embryos as early as day 2 of development. The growth factor nding pattern in several tissues is different than that for insulin binding chick embryo. sulin receptor structure studies have been extended in rat brain. The nding of labeled insulin to thin sections of frozen fresh rat brain was sualized with autoradiography. By several criteria including ructure-activity relationship analysis, the brain insulin receptors were alitatively indistinguishable from insulin receptors previously aracterized on brain and other more typical target tissues and distinct om receptors for the insulin-like growth factors. A distinct pattern with gh levels of binding in all olfactory areas and in only the choroid plexus monstrated a high density of insulin receptors. The data suggest a uromodulatory function for insulin in the brain. Additional studies in tracts of tissues of rodents, Sprague-Dawley rats, ob/ob mice and their in littermates, control and diabetic Chinese Hamsters, have confirmed our evious findings of the presence of an insulin-like material. Although ain and liver membrane receptors are influenced by circulating plasma sulin, the insulin-like tissue content of the same tissues are not fluenced.